Japanese Patent No. 3188507 describes an example of a conventional electric power tool. The electric power tool includes a power supply having a primary battery or a rechargeable secondary battery, a motor, and a control unit for controlling voltage supply from the power supply to the motor.
In the electric power tool, the voltage of the power supply decreases according to use. When the voltage of the power supply decreases, a fastening torque of a working subject component, such as a screw or a bolt, decreases.